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Related Concept Videos

¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...

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Generation and Coherent Control of Pulsed Quantum Frequency Combs
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Strong-interaction-mediated critical coupling at two distinct frequencies.

S Dutta Gupta1

  • 1School of Physics, University of Hyderabad, Hyderabad, India. sdgsp@uohyd.ernet.in

Optics Letters
|June 5, 2007
PubMed
Summary

This study demonstrates enhanced light absorption in a metal-dielectric composite film using a multilayered structure. Nearly all incident light energy is absorbed by suppressing transmission and reflection, achieving critical coupling flexibility.

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Area of Science:

  • Optics and Photonics
  • Materials Science

Background:

  • Critical coupling enables efficient light absorption in optical structures.
  • Metal-dielectric composites offer tunable optical properties.

Purpose of the Study:

  • To investigate light absorption in a novel multilayered medium.
  • To demonstrate enhanced control over critical coupling.
  • To explore the effect of metal inclusion volume fraction on light absorption.

Main Methods:

  • Fabrication of a multilayered medium: metal-dielectric composite film, spacer layer, and dielectric Bragg reflector.
  • Optical characterization to measure transmission and reflection spectra.
  • Analysis of light absorption based on varying metal volume fractions.

Main Results:

  • Achieved nearly total absorption of incident light energy.
  • Demonstrated flexible control over the critical coupling phenomenon.
  • Observed strong light-matter coupling leading to dual-frequency absorption for higher metal volume fractions.

Conclusions:

  • The proposed multilayered structure provides a flexible platform for achieving near-total light absorption.
  • Tuning the metal inclusion volume fraction in the composite film allows for precise control over absorption frequencies.
  • This work has implications for applications requiring efficient light harvesting and sensing.